1. Field of the Invention
This invention relates to polycarbonates and more particularly to mineral filled polycarbonates having high impact properties.
2. Description of the Prior Art
Polycarbonates derived from reactions involving organic dihydroxy compounds and carbonic acid derivatives have found extensive commercial application because of their excellent mechanical and physical properties. These thermoplastic polymers are particularly suited for the manufacture of molded products where impact strength, rigidity, toughness, thermal and dimensional stability as well as excellent electrical properties are required.
In many instances, it is unnecessary to have the maximum strength imparted by a 100 percent polycarbonate resin article and proposals have been made to reduce the strength of the polycarbonate by adding fillers which also reduce the cost of the final article. The balance of reduced cost with reduced physical properties must be somewhat proportionate since small gains in cost reduction with large decreases in impact strength are undesirable.
Typically, a filler level of 5 to 30 percent by weight of the final molded article is acceptable from a cost standpoint, however, typical fillers such as talc, asbestos and similar fillers demonstrate great reductions in impact strength at these filler levels. This degradation in impact and other physical properties is thought to be attributable to the formation of stress concentrations in the vicinity of the individual filler particles causing propagation of cracks in the molded article.
In accordance with the present invention a mineral filled polycarbonate is provided with improved impact strength over conventionally filled polycarbonates.